Method for producing coated calendered paper

ABSTRACT

Several paper grades are finished in a supercalender ( 1 ) or similar calender types in order to increase the smoothness, gloss and other properties of the paper. According to the invention, the method for producing coated and calendered paper or paper board, comprises steps of coating a sheet of paper or paper board and bringing the sheet containing water to a calender ( 1 ), leading the sheet in at least one nip formed by two rolls ( 18, 19 ) of the calender ( 1 ) and imposing simultaneously heat and pressure on the sheet in the nip in order to treat the surface of the web, whereby also water is removed from the sheet, removing water from the sheet before winding in such an extent that the moisture content of the sheet is adjusted to a value of 4.0% or less, leading the treated sheet to a winder ( 21 ), and winding the sheet on a roll.

This application is the national phase under 35 U.S.C. §371 of PCTInternational Application No. PCT/US99/28188 which has an Internationalfiling date of Nov. 30, 1999, which designated the United States ofAmerica and which claims priority to U.S. Ser. No. 09/201590 filed Nov.30, 1999, now abandoned.

The present invention relates to the production and manufacture ofcoated paper grades that are finished especially in a supercalender inorder to increase the smoothness, gloss and other properties of thepaper. The biggest benefits are obtained with a base web that includesat least some mechanical fiber. The improved properties of the printingsurface improve the final quality of the printed sheet. The printabilityof paper and the quality of the printed surface are primary qualityfactors that are valued by the users of paper. Different kinds ofcalendering methods like soft-nip, opti-load and Janus Concept Calendersare used both on uncoated and coated paper grades as well as paper boardgrades.

BACKGROUND OF THE INVENTION

The finest quality of the paper surface has been achieved by treating abase paper sheet by a supercalender. A supercalender comprises aplurality of soft and hard rolls that are arranged on a vertical stackso that each soft roll is between two hard rolls and vice versa. Thestack of rolls can be pressed together in order to produce high linearforces between the contacting surfaces of the rolls. The linear forcesare often called nip forces. The hard rolls can be heated. The smoothingof the paper surface is achieved by simultaneously subjecting the fiberstructure to high pressure and heat. Under the influence of these forcesthe fibers forming the paper reach their glass transit temperature andthe deformation caused by the nip load is permanent. Sliding of thepaper surface on the surface of the rolls also causes deformation of thefibers and increases the smoothing effect. Modern multi-nip calenderscomprise often soft rolls made of polymer compounds and effective meansfor controlling independently the nip loads between each nip of hard andsoft roll. These modern types of calenders have several benefits overthe earlier supercalenders, the main advantages being bettercontrollabilty and runnability.

One important factor that affects the physical behavior of the paper inthe calender nip is the moisture of the base sheet entering thecalender. When the moisture content of the paper increases, the effectof the heat and pressure on the fibers is enhanced and the smoothing andglossing effect is increased. The caliper (thickness) of the paperdiminishes also during calendering and on the wetter parts of the sheetthe reduction of caliper is greater. Therefore, the moisture content ofthe sheet should be even in cross- and machine directions in order toprevent variations of caliper, gloss, smoothness and other properties ofthe sheet. For this reason paper is dried usually to high dryness beforecalendering and it is rewetted for example by steam to a desiredmoisture level. Steam can be also used for leveling the differences ofthe moisture content if information on actual moisture content of thesheet is available.

The control of moisture during manufacture differs on manufacturingcoated and uncoated paper grades. During coating the base web, which hasalready been dried to a desired moisture content during manufacture, iswetted and dried at least twice. The coating mix is a admixture of waterand additives. When the mix is spread on the base web, the web adsorbssome of the water and the water has to be removed from the web bydrying. Coating of both sides of the base web requires two coating anddrying cycles and if multiple coating layers are desired, the number ofcycles increases accordingly. Several wetting and drying cyclesinherently mean that the moisture profile of the web is normally moreeven than the moisture profile of an uncoated sheet that is dried onlyonce. Water absorbed into a coated web exits the web more slowly throughthe coating layer, whereby the fibers absorb more water which causesmore fiber rise in paper of board grades that contain mechanical fiber.

Modern calenders like soft-nip, opti-load and Janus Concept calendersare usually considered modern supercalenders since these also employmultiple calendering nips. These evolution supercalenders feature moresophisticated possibilities to control the nip loads, roll temperatureand sheet moisture than traditional supercalenders. The basic operationprinciple of using high linear load and heat for smoothing the paper isthe same as on supercalenders.

In other types of calenders the nip loads and amount of heat used aresmaller than in supercalenders. Therefore, the quality obtained by thesemethods is not as good as that which is obtainable with supercalenders,but the same physical phenomena occur in all kinds of calenders and theeffect on the fibers is the same. It must be noted that sliding of thepaper on the nip may, in some calender types, have a more significantrole than in a supercalender. Especially so called shoe- or long-nipcalenders, wherein the sheet is pressed on a roll with a specialpressing shoe over a long distance, offer different operationalpossibilities than calenders in which the processing time in each nip isshorter. However, the actual basic method of using the combination ofheat and pressure for finishing the paper surface is always the same.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved methodof producing coated and calendered paper and paper board.

It is another object of the invention to provide a novel apparatus forproducing calendered paper or paper board.

The invention is most suitable for products wherein the base web of theproduct contains mechanical fiber, for example groundwood fiber.

According to the present invention the calendered sheet is dried into amoisture content that is 4.0% or less, preferably 3.5% or less, inparticular 3.2 to 0.1%, calculated from the dry weight of the paper orpaper board.

According to one preferred embodiment of the invention the sheet isdried into a moisture content that is 3.5% or less and remoisturized toa moisture content of 4.0% or less.

According to the other aspects of the present invention, the moisturecontent of the sheet entering the calender from a paper making machine,coater or an unwinder is at least about 3.0%, preferably 3.0 to 8.0%.

The invention is preferably implemented on supercalendered and coatedpaper grades. The invention may also be implemented on other calenderingmethods like soft-nip, opti-load and Janus Concept Calenders and forpaper board.

Other objects and features of the invention will become apparent fromthe following detailed description considered in conjunction with theaccompanying drawings. It is to be understood, however, that thedrawings are intended solely for purposes of illustration and not as adefinition of the limits of the invention, for which reference should bemade to the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematical side view of a supercalender according to theinvention.

FIGS. 2 to 5 are diagrams showing the effect of the end moisture of thecalendered sheet on gloss of printed sheet for some paper grades.

FIGS. 6 to 9 are diagrams showing the effect of the end moisture of thecalendered sheet on print smoothness of printed sheet for some papergrades.

FIG. 10 is a diagram showing the blister resistance of a papermanufactured according to the invention in relation to a referencegrade.

FIG. 11 shows the effect of the moisture content of the sheet on theblistering temperature.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

FIG. 1 shows an off-line calender, wherein the paper is handled asseparate rolls manufactured in paper machine and finished in one orseveral coating stages. The rolls are unwound on an unwinder (not shown)and the paper sheet is lead to a multi-nip supercalender 1. Thesupercalender comprises a plurality of soft 18 and hard 19 rolls andguide rolls 17. The soft rolls 18 are coated with fiber material orsynthetic material. The hard rolls 19 are usually made of steel. Therolls are arranged on a stack wherein each hard roll 18 is between softrolls 19 and the paper sheet is lead through the nips between rolls 18,19 by guide rolls 17 so that it passes through each nip. The calenderalso comprises load cylinders 20 at each end of the rolls 18, 19 forpressing the roll stack together. On the side of the calender 1 are topand bottom dryers 2, 3 for drying the calendered paper. The dryer systemcomprises paper guide rolls 5 and 8 for guiding the paper run 4 betweenthe top and bottom dryers 2, 3. The dryers are positioned to face eachother and any suitable contactless dryer type may be used, for exampleair float, air impingement or infra red dryer. When starting up, athreading tape 6 with tape drive 7 is provided for guiding the leadingedge of the paper sheet through the gap between the dryers along thepaper run 4 while starting up or threading a paper sheet through theprocess.

From the dryers 2, 3 the web is taken under the calender to a winder andthe finished sheet is rewound on a roll 21. The sheet is first taken toa first spreader roll 9 which tensions the sheet in cross-machinedirection in order to prevent crimping of the web. A second spreaderroll 10 positioned upstream from the first spreader roll serves the samepurpose. From the second spreader roll 10 the web is taken through flyrolls 12 to the winder (not shown). A scanner 13 for detectingproperties of the sheet and a moisture detector are positioned on theweb run between the fly rolls and the winder.

An alternative web run is provided directly from the calender 1 throughthe fly rolls 12 to the winder.

The above described embodiment is only one example of severalapparatuses that may be used for implementation of the invention. Forexample, the winder and dryers may be positioned on the same side of thecalender, more than one type of dryers may be used or the calender maybe of some other type than a supercalender. In this specification thecalender is defined to be an apparatus wherein a moving paper or paperboard sheet is treated with heat and pressure. The dryers are preferablyof a contactless type, but cylinder dryers may also be used if sodesired. One important modification is a moisture controlling devicethat can be arranged before the calender. The moisturizing device can bea steam moisturizer, spray moisturizer or a film application devicewherein the water is spread on a roll that runs in contact with the web.Each of these devices is in normal use in paper making industry andfamiliar to a person skilled in the art.

The invention can be implemented with several types of coatingprocesses. The main types of coating methods are blade coating, whereinthe coating mix is leveled of the web by a blade and roll coatingwherein the coating mix is leveled on the web by an applicator roll.Blade doctoring and roll application can be combined and several typesof coaters are included in these general groups. However, the filmtransfer or roll coater process has an advantage over the blade coaters.The film transfer coater or other types of roll coaters stresses the webmuch less than a blade coater whereby the web may contain less chemicalfiber and more mechanical fiber. The strength of the web containing moremechanical fiber is lower than that of the web that contains only orhigh amounts of chemical fiber. The weaker web can be run in a filmcoater much more reliably. The use of mechanical fiber provides abulkier sheet (higher caliper). However the disadvantage of film coateris higher application pressure and application time, whereby more wateris penetrated into the web. This leads to a higher fiber rise duringcoating. Since the web is calendered after coating, this problem isavoided and the invention provides also means for preventing the finerrise during printing. For this reason it is possible to produce a sheetof paper that has the attributes of a sheet having greater basis weight.

The idea of the invention is to control the behavior of the fibers ofthe base sheet and the water content of the sheet so that a good smoothprinting surface is obtained. One quality problem that may occur inprinting of some high quality paper grades is fluting of the sheet inthe printing press. Fluting means that the sheet corrugates in themachine direction in large scale or in several directions in smallscale. In the large scale fluting corrugated waves are formed over largeareas on the sheet and in small scale fluting the waves or deformationsoccur in such a small scale that no actual waves are formed but thesurface of the sheet becomes irregular. The water absorbed causes thedeformation of the sheet from the printing ink to the sheet. Theinvention is based on a surprising discovery that the moisture contentof a calendered sheet has a significant effect on the properties of apaper sheet and the printing quality. Several test were performed inorder to find out the limits of the invention and to achieve betterunderstanding on the theoretical background of the invention. The testresults and theoretical considerations are presented below.

Moisture content tests were performed on different paper grades on rollswhich were run on printing press. One of the major conclusions was thatthe finished sheet moisture content going into the press had asignificant effect on the degree of fluting tendency of the differentsheets of paper. Papers with lower moisture content appeared to fluteless than those with higher moisture content. Two sheets which stood outas having low fluting and low moisture were the S.D. Warren Somersetsheet and the Blandin Intrepid Low Glare sheet. The results from thisfirst press evaluation lead to further investigation into the finishedsheet moisture content and its affect on fluting. It was decided thatthe Blandin Pilot Coater could be utilized to drop the finished sheetmoisture content on a number of different production finished Blandinsheets and that the different conditions would be evaluated on press atRIT (Rochester Institute of Technology). At this stage a number of ideaswere discussed as to how the finished sheet moisture content could belowered in production to decrease fluting tendency.

A second pressroom evaluation was conducted at RIT. In this evaluation aroll of Intrepid Gloss paper in which the finished sheet moisturecontent had been reduced from 4.6% to 1.7% was run on press. Thestandard sheet with the moisture content of 4.6% was also printed forcomparison. When the Blandin sheet with the 1.7% moisture was printed,it was discovered that not only did the sheet have reduced flutingcompared to the standard sheet with 4.6% moisture, but it also hadsignificantly reduced fiber puff and higher ink gloss. On bases of thesetests a third pressroom evaluation conducted to determine how low themoisture content would need to be to get the improved printed surfacecharacteristics.

The third pressroom evaluation was also conducted at RIT. BlandinIntrepid paper with several different moisture content levels was run onpress. All of the paper had been dried on the pilot coater in BlandinResearch, some with Infrared Drying, some with Air Foil Drying, somewith both. Results confirmed that the finished sheet moisture needed tobe under 4.0%, preferably under about 3.0% to acquire all the desiredprinted sheet surface characteristics. Those characteristics includedreduced fluting, reduced fiber puff, and higher ink gloss.

Following the third RIT pressroom evaluation, many different productiontrials were conducted in an effort to better understand the invention.Finished production paper was dried to below a 3.0% moisture either onthe pilot coater or in production on the new 4A production coater. Paperwas also dried to a lower moisture off the coater resulting in a lowermoisture content off of the supercalenders. It was found that paperdried to a lower moisture content off the coater did not print assmoothly as paper dried to a higher moisture content off the coater.These trials show that a higher moisture content off the coater isrequired so that the sheet has the plasticity that it needs to smoothenits surface as it goes through the supercalender. It was concluded thatto have a smooth print surface, you must start with a smooth unprintedsurface, in other words the surface quality of the unprinted paper hasan impact on the final printing result. Many different pressroomevaluations were conducted on trial rolls manufactured according to theinvention to better understand the concept and the optimization limitsand parameters. During these trials, several additional benefits of theinvention were discovered-and capital requirements were also identifiedfor the addition of dryers to the supercalenders on a production papermachine line. A drying system was designed to apply the invention inproduction scale and the drying system is currently operational.

Results of the trials and test show that the invention, when applied tothe finished sheet and then printed, improves the sheet quality a numberof ways:

it reduces fiber puff and fiber rise improving printed sheet smoothnessand ink gloss.

it reduces ink absorption improving ink gloss and reducing inkconsumption,

it improves the sheets dimensional stability and reduces printed sheetfluting,

it improves the sheet moisture profile and roll quality,

it reduces blistering tendency, and

it allows for a reduction in printed sheet ink mottle.

It is well known that running a lower moisture content in the finishedsheet improves the sheet moisture profile. It is also well known thatthe lower the moisture content of the finished sheet going into thepress, the less tendency the sheet will have to blister due to lessmoisture trying to escape through the sealed surface layer. What is notwell understood is the affect of low moisture content on mechanicalfiber, like groundwood fiber puff and fiber rise, improved ink gloss,reduced fluting, and binder migration mottle reduction. The theorybehind each of these attributes is explained in following on bases ofliterature study, experimental analysis, and production trial and errorin view of the present understanding of the invention.

Improvements seen in printed sheet smoothness and fluting tendencyreduction of groundwood containing papers during offset printing as aresult of the application of the invention are due to reduced waterpenetration into the sheet and reduced water expansion within the sheet.In web offset printing, water is applied to the surface of the sheet.Some of this water penetrates into the sheet and interacts with thefibers causing stress relaxation of the internal structural components,swelling of the fibers, and debonding of the fibers through dissolutionor weakening of the fiber-fiber bonds. When coated paper is dried andcalendered, the fibers within the sheet are flattened into a ribbonshape. When these fibers are re-wetted in the offset press, they swell.Chemical kraft fibers, though they swell when wetted, will maintaintheir flat ribbon shape and have minimal effect on the printed sheetsmoothness. Groundwood fibers, when re-wetted during the offset printingprocess, will swell and transition from their ribbon shape to a tubeshape. This transition is the result of water expansion (water changingfrom a liquid to gaseous state) during the drying phase of the offsetprinting process. Once the groundwood fiber has expanded, the ligninrich cell fiber wall stiffens and maintains this tube shape resulting inwhat we call fiber puff. If the groundwood fiber or part of the fiber islocated near, or protruding from the surface of the sheet, the fiberappears to stick out from the surface of the sheet and this is calledfiber rise. It is this fiber puff and fiber rise which causes asignificant amount of sheet roughness and reduced ink gloss. It is clearthat problems related to the fiber rise increase when the thickness ofthe coating layer decreases. Therefore the control of fiber rise onproducts comprising 1-5 g/m² coating per side, so called Ultra LightWeight Coated (ULWC) grades, is extremely important. The inventionprovides a good method for producing ULWC papers and boards also byusing base web containing mechanical fiber by control of the fiber rise.The main principle how the invention controls the fiber rise is dryingof the coated web into a very low moisture content whereby the fibers donot absorb water easily during the short moisturizing cycle of theprinting process.

The problem with using higher moisture of the web when the web entersthe calender is that it is extremely difficult to maintain good moistureprofile of the web when it is not dried to a moisture of 3-4%. Themoisture content that the invention preferably requires is 6-8% orpreferably even more. These values are difficult to achieve simply bycontrolling the drying process of the paper machine. According to theinvention the web is coated before calendering. The web can be normallydried as dry as desired, for example to a moisture content of 3.5-4%,and the water in the coating mix provides the water that raises themoisture content of the web to a desired level and the moisture contentcan be easily controlled by line measurement apparatus and bycontrolling the coating profile. Modern coating apparatus use normallydryers wherein the drying power can be controlled crosswise over theweb, which provides an effective means for keeping the moisture of theweb even and on a desired value.

Water which is bound within the sheet structure, and not necessarilywithin a fiber, can cause a considerable amount of sheet rougheningalso. When water and/or ink is applied to the surface of the sheet inthe offset printing process, it seals the coating layer and hinderswater (or gas) evaporation from the sheet during the drying process. Thebound water will expand during the drying process resulting in adissolution of the internal and external structure of the sheet. Smallcracks in the coating layer can also be the result of this bound waterexpansion. These small cracks also contribute to print surfaceroughening, ink gloss reduction, and sheet surface dissolution. Thisinternal and external sheet dissolution, because it disrupts the entiresheet structure, contributes to a loss of dimensional stability in thesheet which in turn results in printed sheet fluting.

The invention removes a significant portion of the internal and fiberbound water from the sheet structure prior to the printing press thusdecreasing this internal and external sheet dissolution. Water removalfrom the finished sheet during the paper making process does not disruptthe internal or external sheet structure because the surface of thesheet has not been sealed and gaseous moisture vapor escapes freely.Because the moisture content of the sheet has decreased, the penetrationrate of additional water into the sheet is reduced when the paper isprinted on press. This phenomena is partly explained by the fact thatmost of the substances absorb water more easily if slightly wetted andhave in a very dry state a hydrophobic character.

Tests conducted by the applicant at the Research laboratory at BlandinPaper show that reducing the finished sheet moisture content, accordingto the preferred embodiment of the present invention, to under 3.2% orin particular under 3.0% actually “sized” the surface of the sheet andreduced the rate of water penetration into the sheet. The word “sizing”in paper making industry means sealing the surface or increasing thestrength of a paper or board usually by impregnating the surface withstarch-based or other suitable substance. Water induced fiber expansionis decreased resulting in reduced groundwood fiber puff, fiber rise, andsheet dissolution. Because the fiber structure is maintained and watermovement into and out of the sheet is reduced, fiber to fiber bonding ismaintained and stress relaxation is significantly reduced. It is thisstress relaxation and overall fiber distortion reduction which reducesthe fluting tendency of the sheet. With less internal distortion, thesheet maintains more dimensional stability through the entire printingprocess resulting in the reduction in fluting.

Ink gloss enhancement results in part from the printed sheet smoothnessimprovement. The smoother surface allows for more even ink distributionon the sheet surface resulting in ink gloss improvement. Ink glossenhancement is also the result of a reduced ink setting rate orabsorbency of ink vehicle oil. Because the moisture content of thefinished sheet has been reduced prior to the addition of ink, the inkabsorbency rate has also been decreased. Fast ink setting rate causes areduction in print gloss. High absorbency of the ink vehicle oil intothe coating allows less time for the ink to flow to its ideal level onthe paper surface. High absorbency also produces a rougher ink filmresulting in lower print gloss. A lower ink absorbency rate allows for areduced ink setting rate which results in a smoother ink film and thusimproved ink gloss.

One of the additional benefits of the invention and one of its preferredembodiments is the affect on print binder migration mottle and processchanges which allow for additional optimization of printed sheetsmoothness. As mentioned earlier in this paper, trials were conducted inproduction to see if the finished sheet moisture could be reduced bylowering the sheet moisture off the coater and going to thesupercalender. We found that as we lowered the sheet moisture going tosupercalender, we roughened the finished sheet coming off thesupercalender. As a result, even though the finished sheet moisture waslower, the white paper was so rough that the print surface was rougheralso. What the invention allows for is that we can now run the coatermoisture up higher and improve the white paper smoothness off thesupercalender. In the past, this would have meant a higher moisturecontent off the supercalenders which would have created a number ofproblems in the pressroom. By reducing the total finished sheet moisturecontent after running a higher moisture into the supercalender, we areable to optimize and achieve additional improvement in printed sheetsmoothness. It was also determined that by running a higher sheetmoisture off the coater, coater drying rates were reduced, resulting inless coating binder migration on the coater. Less coating bindermigration has been proven to significantly effect finished sheet printmottle on paper produced.

In an apparatus described in FIG. 1, wherein the paper is dried with aseparate dryer after calendering, the typical limits for moisturecontent after coating and before entering the calender are about 3.0 to8.0%, after calendering about 2.5 to 7.0% and after drying the finalmoisture content of the finished sheet is 0.0 to 4.0%, preferably 3,5%whereafter the paper is remoisturized to a moisture content between0.5-4.0%. The typical favorable moisture contents used for Blandin glossgrade papers are 6.0% off the coater, 4.7% off the supercalender and2.8% after drying and remoisturizing with a AM Technology process(AM=altered moisture) respectively.

The purpose of the remoisturizing is to finally level out possiblevariations in the moisture of the sheet and adjust the moisture of thesheet to a level best suitable for the printing method wherein the paperis to be used. However, the final moisture of the sheet may not exceed avalue wherein the fibers absorb water or their hydrophobic propertiesobtained by drying after calendering will deteriorate. Theremoisturizing of the dried sheet can be accomplished by applying waterin a spray or film or preferably by using water vapor or humid air. Theremoisturizing can be performed before winding or rolls may be set tomoisturize in a humid atmosphere after winding.

FIGS. 2 to 5 show print glosses of different paper grades on differentfinal moisture contents. The paper grades used in the comparison were40# INTREPID, 45# INTREPID, 60# INTREPID and 50# GRAND IMPRESSION. Theleft columns show gloss of the top side of the sheet and the rightcolumns show the glosses of the wire side of the sheet. It can be seenfrom all of the figures that decreasing the moisture content to 3.2% orless gave significantly better print gloss values compared to a controlsample having a moisture content of, for example 4.5%. It also can beseen that if the moisture content is further decreased, the print glossvalues did not increase or did decrease slightly. On bases of these testresults it can be deducted that the optimum moisture content fordifferent paper grades is about 3.0%.

The FIGS. 6 to 9 show the effect of altered moisture content to Parkerprint smoothness. The same paper grades as mentioned above were used inthe evaluation. In smoothness scale smaller values describe bettersmoothness, i.e. smaller values indicate smoother surface. Also here itcan be seen that decreased moisture of the sheet gives significantlybetter smoothness and further decreasing the moisture content does notusually give better smoothness. One further feature is that thedifference in smoothness of top side and wire side of the sheet usuallychanges when moisture is decreased in comparison to the control samples.

FIGS. 10 and 11 show results blistering tests on 60#INTREPID and GRANDIMPRESSION GRADES. Blistering is a phenomenon wherein water evaporatingwithin a paper or cardboard sheet disintegrates the surface of thesheet. As can be seen from FIG. 10, the ALTERED MOISTURE INTREPID (AMINTERPID) produced according to the invention has a considerably higherblistering temperature and resistance than standard INTREPID. FIG. 11shows clearly that when the moisture content is decreased, theblistering temperature increases almost linearly. Note that the diagramshows both target and actual moisture contents and the curve between 3.1and 2.4% actual moisture is slightly steeper. However, more measurementpoints would be needed to surely show more rapid increase in blisteringtemperature when moisture content is lowered below 3.1%, but the diagramgives at least an indication of probable results.

According to the invention, a paper or board sheet is handled in acalender which is preferably a supercalender or alternatively animproved calender designed on basis of the supercalender operatingprinciples. Suitable calender types have been mentioned above. Aftercalendering the sheet is dried in a separate dryer before winding to amoisture content that is 4% at highest and preferably about 3.0%. Itmight be possible to adjust the final moisture content in the calenderto above mentioned value, but then the calendering result may not be asgood as when separate drying step is used. Also the temperature controlof the heated rolls of the calender may be more difficult if very drypaper is produced without drying after the sheet is handled in thecalender. The invention may be implemented on other calender types also,but the benefits may not be as great as when implemented onsupercalendered papers since the smoothness of paper grades thusproduced is not as good as that of grades made by supercalendering orsimilar high-gloss calendering methods. The invention is preferablyimplemented on paper grades based on groundwood base sheet that iscoated with at least one coating layer. However, it is possible toimplement the invention also to grades based on chemical kraft and foruncoated grades and also for paper board. The supercalender isadvantageously arranged on-line with a coater, but the paper can bebrought to the calender from an unwinder or directly from a paper orboard machine.

The drying of the paper or board sheet and remoisturizing can also beperformed in a separate step by unwinding the calendered and wound sheetand drying and/or remoisturizing the sheet, whereafter the sheet can bedirectly printed or rewound on a roll. This method makes it possible tohandle the sheet directly before printing in a desired manner.

Thus, while there have been shown and described and pointed outfundamental novel features of the invention as applied to a preferredembodiment thereof, it will be understood that various omissions andsubstitutions and changes in the form and details of the invention maybe made by those skilled in the art without departing from the spirit ofthe invention. For example, it is expressly intended that allcombinations of those elements and/or method steps which performsubstantially the same results are within the scope of the invention.Substitutions of the elements from one described embodiment to anotherare also fully intended and contemplated. It is also to be understoodthat the drawings are not necessarily drawn to scale but they are merelyconceptual in nature. It is the intention, therefore, to be limited onlyas indicated by the scope of the claims appended hereto.

What is claimed is:
 1. A method for producing calendered paper orpaper-board, comprising steps of manufacturing a web base sheet of paperor board, coating the web base sheet with at least one coating layer sothat water is absorbed in the web, bringing the base sheet containingwater to a calendar, leading the web base sheet through at least one nipformed by two rolls of the calender and imposing simultaneously heat andpressure on the web base sheet in the nip in order to treat the surfaceof the web, whereby also water is removed from the sheet, drying toremove water from the web base sheet before printing to such an extentthat the moisture content of the sheet is adjusted to a value of 0.0 to4.0%, remoisturizing the sheet after calendering and drying to amoisture content of 0.0 to 4.0%, leading the treated sheet to a winder,and winding the sheet on a roll.
 2. The method according to claim 1,wherein the web base sheet is dried with at least one dryer aftercalendering and before winding.
 3. The method according to claim 2,wherein the calender is a supercalender.
 4. The method according toclaim 2, wherein the calender is a soft-nip, opti-load or a JanusConcept Calender.
 5. The method according to claim 1, herein the coatinglayer of the web base sheet has a final coat weight of 1-5 g/m².
 6. Themethod according to claim 1 wherein the web base sheet is coated with aroll coater, or a film transfer coater.
 7. The method according to claim1, wherein the moisture content of the web base sheet before calenderingis 3.0 to 8.0%.
 8. The method according to claim 2, wherein the moisturecontent of the web base sheet after calendering and before drying isadjusted to a value of between 2.5 to 7.0%.
 9. The method according toclaim 1 wherein the sheet is coated with a blade coater.
 10. The methodaccording to claim 1, wherein the sheet is remoisturized before winding,with water, water spray, steam or humid air.
 11. The method according toclaim 1, wherein the sheet is remoisturized before winding with steam orhumid air.
 12. The method according to claim 1, wherein the drying andremoisturizing of the web base sheet is effected after unwinding the webbase sheet from the roll and prior to printing.
 13. The method accordingto claim 1, wherein the remoisturizing of the web base sheet is effectedafter unwinding the web base sheet from the roll and prior to printing.14. The method according to claim 11, wherein prior to winding themoisture content of the web base sheet is adjusted to a value of 0.0 to3.0%.
 15. A method for producing calendered paper or paperboard whichcomprises manufacturing a web base sheet of paper or board, coating theweb base sheet with at least one coating layer whereby water is absorbedin the web, calendering the web base sheet by conveying it through acalender containing at least one nip formed by opposing rolls, whereinheat and pressure is applied to the web base sheet at the nip and somewater is removed therefrom, drying the web base sheet to a moisturecontent of 0.0 to 4%, and remoisturizing the web base sheet to amoisture content of 0.0 to 4%.
 16. The method of claim 15 wherein aftercoating but before entering the calender, the water content is about 3to 8%.
 17. The method of claim 16 wherein after calendering, the watercontent is about 2.5 to 7%.
 18. The method of claim 17 wherein afterdrying, the water content is about 0.0 to 4.0%.
 19. The method of claim18 wherein after remoisturizing, the moisture content is between 0.5 to4.0%.
 20. A method for producing calendered paper or paper board whichcomprises manufacturing a web base sheet of paper or board, coating theweb base sheet with at least one coating layer whereby water is absorbedin the web, calendering the web base sheet by conveying it through acalender containing at least one nip formed by opposing rolls, whereinheat and pressure is applied to the web base sheet at the nip and somewater is removed therefrom, winding the web base sheet as a roll,unwinding the web base sheet, drying the web base sheet, andremoisturizing the sheet prior to printing.
 21. The method of claim 20wherein the web base sheet is remoisturized to a moisture content of4.0% or less.
 22. A method for producing calendered paper or paper boardwhich comprises manufacturing a web base sheet of paper or board,coating the web base sheet with at least one coating layer whereby wateris absorbed in the web, calendering the web base sheet by conveying itthrough a calender containing at least one nip formed by opposing rolls,wherein heat and pressure is applied to the web base sheet at the nipand some water is removed therefrom, remoisturizing the sheet prior toprinting.